Nelson, Philip C2023-05-232023-05-232018-07-232018-05-26https://repository.upenn.edu/handle/20.500.14332/43387This chapter extends Part III of the book From Photon to Neuron (Princeton Univ Press 2017). This preliminary version is made freely available as-is in the hope that it will be useful.Copyright 2018 by Philip C Nelson.Physical Sciences and MathematicsPhysicsBook Chapter